The objective of this study is to determine the chemical structure and mechanism of action of two forms of Staphylococcal alpha toxin isolated from Woods strain 46. The first aspect will include ordering of peptides obtained by CNBr and enzymatic cleavage of the proteins leading eventually to a complete amino acid sequence. These studies should permit a direct comparison of the two forms of alpha toxin leading to an assessment of conserved and presumably essential portions of the toxin. Peptide competition studies will be undertaken to localize those portions of the molecule involved in antibody binding and in membrane binding. Studies on the biological properties of alpha toxin include selective chemical modification of alpha toxin to determine which amino acids are essential for function. Various lipids and other membrane components will be tested for their capacity to bind to alpha toxin and to inhibit the activity of the toxin. Binding will be assessed by equilibrium measurements and by measurement of induced changes in conformation, while effects on activity will be assessed by hemolytic assay. The stoichiometry of binding of alpha toxin to RBC membranes from various species will be investigated. These studies include the effects of enzymatic and chemical modifications of the membranes on their capacity to bind toxin. The binding "surface" of the toxin will be evaluated by examining the distribution of radiolabel in tryptic peptides obtained after I131 iodination of native and membrane bound toxin. Studies to establish the conditions necessary for dissociation of toxin from membranes are planned.